Some people have found the thumb to be tight in this pattern. i suggest knitting 5+ rows of the thumb and trying it on. if you find it VERY tight, rip back to beginning of thumb and adding 2 additional stitches to the thumb OR knitting additional increase rows to increase the size of the gusset.

However, if you find the thumb just a little tight, I would leave it. The thumb on my sample has loosened up a lot with wearing.